Populations and Evolutions

Question 1

species

Answer 1

group of organisms that can interbreed and produce fertile offspring

Question 2

population

Answer 2

all the organisms of a particular species that live in same area

Question 3

gene pool

Answer 3

the range of different alleles existing for a particular locus within a population

Question 4

allele frequency

Answer 4

proportion of a certain allele within a gene pool, expressed as a decimal or percentage

Question 5

Hardy-Weinberg principle

Answer 5

allows us to estimate the frequency of alleles in a population, as well as if the allele frequency is changing over time.

Question 6

assumptions made by Hardy-Weinberg principle

Answer 6

-no mutations occur to create new alleles
-no migration in or out of the population
-no selection, so alleles are all equally passed to next generation
-random mating
-large population

Question 7

Hardy-Weinberg equation for calculating allele frequency

Answer 7

the frequencies of each allele for a characteristic must add up to 1.0
p+q=1
p=frequency of dominant allele
q=frequency of the recessive allele

Question 8

Hardy-Weinberg equation for calculating genotype frequency

Answer 8

the frequencies of each genotype for a characteristic must add must add up to 1.0.
p² + 2pq + q² = 1
p²=frequency of homozygous dominant
2pq=frequency of heterozygous
q²=frequency of homozygous recessive

Question 9

genetic factors that cause phenotypic variation within a species

Answer 9

-mutation of alleles
-random fertilisation by gametes
-random assortment by genetic material during meiosis

Question 10

why does natural selection occur?

Answer 10

-predation
-disease
-competition
all resulting in differential survival and reproduction

Question 11

How does natural selection cause a change in a population’s gene pool over generations

Answer 11

organisms with advantageous alleles more likely to survive and pass on their favourable alleles to future offspring. Allele frequency of of advantages alleles increases, frequency of unfavourable alleles decrease.

Question 12

stabilising selection

Answer 12

-when environmental conditions stay the same
-individuals closest to the mean are favoured, and any new characteristics are selected against.
-results in low diversity

Question 13

directional selection

Answer 13

-occurs when environmental conditions change
-individuals with the phenotypes better suited to the new conditions more likely to survive and reproduce-pass on their genes
-overtime the mean of the population will move towards these characteristics

Question 14

disruptive selection

Answer 14

-occurs in fluctuating environments which favor more than one type of phenotype
-individuals with alleles of both extreme phenotypes favoured over the mean-more likely to survive and reproduce
-over time, the population becomes phenotypically divided

Question 15

natural selection

Answer 15

the process which organisms better adapted to their environment survive and reproduce and pass on their advantageous alleles to their offspring, whilst those less well adapted fail to do so.

Question 16

speciation

Answer 16

when a new species arises from an existing species due to different selective pressures.
It occurs when populations of the same species become reproductively isolated from each other- can no longer interbreed and produce fertile offspring.

Question 17

allopatric speciation

Answer 17

-speciation resulting from a physical barrier.
-different environmental conditions-so populations affected by different selection pressures
-so different advantageous alleles are favoured and passed on, producing different phenotypes in two groups
-no longer able to reproduce as the populations become very different resulting in speciation

Question 18

sympatric speciation

Answer 18

speciation resulting from a non physical barrier e.g. mutation that no longer allows two organisms to produce fertile offspring
-random mutation/ change in behavious prevents it from breeding with others that do not have the same mutation/behaviour.

Question 19

genetic drift

Answer 19

-a change in population’s allele frequencies that occurs due to chance rather than selective pressures .
-by chance an allele for one genotype is passed on to more offspring than the other-> no. individuals with this allele increases
-if by chance this same allele is passed on more often over repeated generations then this can lead to evolution as the allele changes in frequency in the population.

Question 20

why does genetic drift affect small populations more than large ones?

Answer 20

-the gene pool is smaller so there are less alleles available, any change in frequency becomes pronounced very quickly.